Bottom Line:
We additionally provide new structural and biochemical evidence of PfUIS3(130-229) interactions with lipids (phosphatidylethanolamine), with phospholipid liposomes, and with the human liver fatty acid-binding protein.The direct interaction of PfUIS3(130-229) with liver fatty acid-binding protein most likely provides the parasite with a conduit for importing essential fatty acids/lipids.Therefore, our analyses have implications for lipid transport into the parasite during the rapid growth phases of sporozoites.

ABSTRACTMalaria parasite UIS3 (up-regulated in infective sporozoites gene 3) is essential for sporozoite development in infected hepatocytes. UIS3 encodes for a membrane protein that is localized to the parasite parasitophorous vacuolar membrane in infected hepatocytes. We describe here 2.5-A resolution crystal structure of Plasmodium falciparum UIS3 soluble domain (PfUIS3(130-229)) in complex with the lipid phosphatidylethanolamine (PE). PfUIS3(130-229) is a novel, compact, and all alpha-helical structure bound to one molecule of PE. The PfUIS3(130-229)-PE complex structure reveals a novel binding site with specific interactions between PfUIS3(130-229) and the PE head group. One acyl chain of PE wraps around part of PfUIS3(130-229) and docks onto a hydrophobic channel. We additionally provide new structural and biochemical evidence of PfUIS3(130-229) interactions with lipids (phosphatidylethanolamine), with phospholipid liposomes, and with the human liver fatty acid-binding protein. The direct interaction of PfUIS3(130-229) with liver fatty acid-binding protein most likely provides the parasite with a conduit for importing essential fatty acids/lipids. Therefore, our analyses have implications for lipid transport into the parasite during the rapid growth phases of sporozoites. Given that PfUIS3 is essential for establishment of liver stage infection by P. falciparum, our data provide a new target for abrogating parasite development within liver cells before typical symptoms of malaria can manifest.

fig11: Model of molecular cross-talk between PfUIS3 and fatty acids/lipids. PfUIS3 is resident on the PVM, and its larger, soluble domain is exposed to the contents of the hepatocyte cytoplasm. PfUIS3130-229 adopts a four α-helix bundle that cannot only bind to LFABP but also directly interact with lipids. These twin abilities suggest that PfUIS3 may be a critical molecular motor for lipid import into the parasite.

Mentions:
In the aqueous environment of the liver hepatocyte cytosol, the presence of free fatty acids is unlikely because of their hydrophobic character. The parasite seems to have therefore developed molecular machinery that can act as a conduit for stepwise capture and transfer of fatty acid, thereby obviating the requirement for extensive lipid synthesis within the parasite. The likely mechanism of interaction (Fig. 11), based on structures of LFABP and PfUIS3130-229 may be: (a) LFABP shuttles fatty acids/lipids from host cytoplasm to UIS3, (b) UIS3 binds directly to LFABP and captures its cargo in a continuous and dynamic fashion, (c) UIS3 ligand-binding sites undergo conformational changes to accommodate fatty acids/lipids, and finally, (d) similar to the collisional transfer mechanism used by other fatty acid transporters, the membrane tethered UIS3 releases its cargo directly on to the parasite PVM. Repetition of this transfer cycle will ensure a ready supply of LFABP cargo to the growing parasite within the host liver cell; the absence of UIS3 therefore robs the parasite of a molecular intermediary capable of scavenging LFABP cargo.

fig11: Model of molecular cross-talk between PfUIS3 and fatty acids/lipids. PfUIS3 is resident on the PVM, and its larger, soluble domain is exposed to the contents of the hepatocyte cytoplasm. PfUIS3130-229 adopts a four α-helix bundle that cannot only bind to LFABP but also directly interact with lipids. These twin abilities suggest that PfUIS3 may be a critical molecular motor for lipid import into the parasite.

Mentions:
In the aqueous environment of the liver hepatocyte cytosol, the presence of free fatty acids is unlikely because of their hydrophobic character. The parasite seems to have therefore developed molecular machinery that can act as a conduit for stepwise capture and transfer of fatty acid, thereby obviating the requirement for extensive lipid synthesis within the parasite. The likely mechanism of interaction (Fig. 11), based on structures of LFABP and PfUIS3130-229 may be: (a) LFABP shuttles fatty acids/lipids from host cytoplasm to UIS3, (b) UIS3 binds directly to LFABP and captures its cargo in a continuous and dynamic fashion, (c) UIS3 ligand-binding sites undergo conformational changes to accommodate fatty acids/lipids, and finally, (d) similar to the collisional transfer mechanism used by other fatty acid transporters, the membrane tethered UIS3 releases its cargo directly on to the parasite PVM. Repetition of this transfer cycle will ensure a ready supply of LFABP cargo to the growing parasite within the host liver cell; the absence of UIS3 therefore robs the parasite of a molecular intermediary capable of scavenging LFABP cargo.

Bottom Line:
We additionally provide new structural and biochemical evidence of PfUIS3(130-229) interactions with lipids (phosphatidylethanolamine), with phospholipid liposomes, and with the human liver fatty acid-binding protein.The direct interaction of PfUIS3(130-229) with liver fatty acid-binding protein most likely provides the parasite with a conduit for importing essential fatty acids/lipids.Therefore, our analyses have implications for lipid transport into the parasite during the rapid growth phases of sporozoites.

ABSTRACTMalaria parasite UIS3 (up-regulated in infective sporozoites gene 3) is essential for sporozoite development in infected hepatocytes. UIS3 encodes for a membrane protein that is localized to the parasite parasitophorous vacuolar membrane in infected hepatocytes. We describe here 2.5-A resolution crystal structure of Plasmodium falciparum UIS3 soluble domain (PfUIS3(130-229)) in complex with the lipid phosphatidylethanolamine (PE). PfUIS3(130-229) is a novel, compact, and all alpha-helical structure bound to one molecule of PE. The PfUIS3(130-229)-PE complex structure reveals a novel binding site with specific interactions between PfUIS3(130-229) and the PE head group. One acyl chain of PE wraps around part of PfUIS3(130-229) and docks onto a hydrophobic channel. We additionally provide new structural and biochemical evidence of PfUIS3(130-229) interactions with lipids (phosphatidylethanolamine), with phospholipid liposomes, and with the human liver fatty acid-binding protein. The direct interaction of PfUIS3(130-229) with liver fatty acid-binding protein most likely provides the parasite with a conduit for importing essential fatty acids/lipids. Therefore, our analyses have implications for lipid transport into the parasite during the rapid growth phases of sporozoites. Given that PfUIS3 is essential for establishment of liver stage infection by P. falciparum, our data provide a new target for abrogating parasite development within liver cells before typical symptoms of malaria can manifest.